The Blues have won only once in the league in their first season back at their Cardiff Arms Park home.
It was a tryless, error-strewn affair to set before a season's best 9,872 crowd, the home fans heading for the bars disappointed.
They had started the evening with renewed optimism, with Wales lock Bradley Davies returning from injury and flying wing Alex Cuthbert having just signed a three-year contract extension.
But the Scarlets also welcomed back injured internationals in back-row duo Josh Turnbull and Aaron Shingler while, even without fly-half Rhys Priestland, their back division still included five of Wales' current squad.
And Shingler in particular shone as his team deservedly took the spoils.
There was little imagination in the early exchanges, with aimless kicks the order of the day. With the Blues scrum soon under pressure, the Scarlets were awarded two penalties in the first 10 minutes and fly-half Aled Thomas slotted over both, the second from some 50 yards.
His opposite number, teenager Rhys Patchell - touted in some quarters as a possible replacement for Priestland in the Wales number 10 shirt - started shakily with a clearance kick charged down by lively hooker Emyr Phillips but made no mistake when referee Ian Davies penalised the visitors for obstruction.
The Blues were given a let-off when Thomas pushed the easiest of his penalty chances wide, but Patchell was guilty of an even worse miss from in front of the posts.
The Scarlets showed some adventure when prop Phil John burst through in the home 22 but the move broke down and they had to settle for another Thomas penalty in the final significant action of a tedious half.
There was a little more rugby to open the second period, with the West Walians throwing the ball around in a series of crossfield moves, but the Blues defence held firm and they eventually turned over possession, a lengthy touchfinder by full-back Jason Tovey sending play deep into Scarlets territory.
But it was soon back to the boot, with Patchell halving the deficit, as any likelihood of the game developing a flow was not helped by repeated stoppages for minor injuries to be treated.
Even the place-kicking was being affected by the general mediocrity, Thomas missing another straightforward penalty.
When big wing George North finally had half an opening, the Blues were able to snuffle out the attack and when the Scarlets found space on the left, Thomas ruined it by hurling a wildly forward pass to the unmarked Liam Williams. It summed up a match that will be quickly forgotten.
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